[PATCH] D86796: [Sema] Address-space sensitive index check for unbounded arrays

[Bevin Hansson via Phabricator via cfe-commits]

ebevhan added inline comments.


================
Comment at: clang/lib/Sema/SemaChecking.cpp:13981
+        bool overflow;
+        llvm::APInt product(index);
+        product += 1;
----------------
ebevhan wrote:
> chrish_ericsson_atx wrote:
> > ebevhan wrote:
> > > What if index is wider than AddrBits, but the active bits are fewer? Then you might miss out on triggering the overflow case in the multiplication.
> > Line 13984 checks for active bits of product being less than AddrBits, which is the same case (since product, by definition, has same width as index).  So I think this is covered.  If I've misunderstood, please re-ping.
> The overflow limit for _ovf is determined by the width of the APInt. If index is 32 bits wide but only has 14 bits active, and AddrBits is 16, then an umul_ovf might overflow past 16 bits but not for 32 bits since the product is the same width as the index. Then we won't detect the overflow.
Scratch this; I missed the second getActiveBits check. With that it should be fine.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86796/new/

https://reviews.llvm.org/D86796